Sears has a 1000/1200# one that will work fine and staying away from Harbor Frieght is a good idea.
Any muffler will work as good as another, new or used. Look on e-bay and get a deal. When you assemble the system have the Muffler Shop run the pipes 'side by side' unconnected to the mufflers. After that you can put the tail pipes anywhere you like.
Take your time , get a good deal.
